One-step Beckmann Rearrangement from Ketones and Hydroxylamine in Dry Media under Microwave Irradiation

TheBeckInannrearrangement,theacid-mediatedisomerizationofoximestoamides,wasfirstdiscoveredinl886l.Asoneoftheoldestandmostfamiliartransformationsinorganicchemistry,ithasbeenwidelystudiedandagreatvarietyofmethodstoconductthistfansformationhavebeenreported'.However,mostofthesemethodswerecarriedoutbyusingalargeamountofsolventswithlongreactiontime.Whatismore,thepriorpreparationofthecorrespondingketoximesisusuallyrequired,whichmakestheseprocessesinconvenientandlessattractive.Bytakingadvantageofboth…     

P2O5/SiO2‐Catalyzed One‐Pot Synthesis of Amides from Ketones via Schmidt Reaction under Microwave Irradiation in Dry Media

A facile and efficient method for the preparation of amides from ketones by the Schmidt reaction is described for the first time using P₂O₅/SiO₂ and sodium azide under solvent‐free microwave irradiation. Advantages of this procedure are selectivity, good yields, a simple operation, short reaction time, and solvent‐free conditions.     

One‐Pot Synthesis of Iminoimidazolines under Microwave Irradiation in Solvent‐Free Conditions

Substituted iminoimidazolines were synthesized from a one‐pot reaction of aromatic or hetero‐aromatic amines with imidazolidine‐2‐thione under solvent‐free conditions using microwave irradiation with good to excellent yields.     

Clean,One‐Pot Synthesis of Naphthopyran Derivatives in Aqueous Media

A general and practical one‐pot synthesis of naphthopyran derivatives using hexadecyltrimethylammonium bromide (HTMAB) as catalyst (10 mol%) is described. This method provides several advantages such as neutral conditions, high yields and simple workup procedure. The catalyst is low cost, facile, active, environmentally friendly, and reusable. In addition, water is chosen as a green solvent.     

One‐Pot Synthesis of 2‐Acylimino‐3‐aryl‐thiazoline Derivatives in Aqueous Media

A one‐pot, two‐step synthesis for acyliminothiazolines by treated N,N′‐substituted thioureas with α‐bromocarbonyl compounds under aqueous media was described. Compared to the classical reaction in organic solvents, this method consistently has the advantage of short reaction times, convenient procedures, and mild reaction conditions.     

Synthesis of Substituted 1,4‐Dihydropyridines in Water Using Phase‐Transfer Catalyst Under Microwave Irradiation

Abstract

The synthesis of various substituted 1,4‐dihydropyridines has been achieved by the reaction of aldehydes, ethyl/methyl acetoacetates, and ammonium acetate in water using phase‐transfer catalyst under microwave irradiation. Compared to the classical Hantzsch's reaction conditions, this new method consistently has the advantage of good yields and short reaction times. Bifunctional compounds containing two units have been synthesized using dialdehyde as precursor in good yields.     

One‐Pot Wittig Reactions in Aqueous Media: A Rapid and Environmentally Benign Synthesis of α,β‐Unsaturated Carboxylic Esters and Nitriles

One‐pot Wittig reactions of ethyl bromoacetate and bromoacetonitrile with aldehydes in the presence of PPh₃ and LiOH in water were investigated. Most of the olefination reactions completed within 5–120 min in refluxing water containing 1.2 M LiCl to afford the olefin products in 71–97% yields with 100:0–55:45 ratios of E:Z isomers.     

Rapid One-Pot Synthesis of Alkane-α,ω-Diylbisphosphonic Acids from Dihalogenoalkanes Under Microwave Irradiation

A one-pot, two-step synthesis of alkylenebisphosphonic acids from dihalogenoalkanes was performed under microwave irradiation. The reaction is very rapid and convenient for the synthesis of small samples of alkylenebisphosphonic acids.     

Microwave Assisted Synthesis of Fluorinated Hexahydro 1,3,5‐Triazine Derivatives in Aqueous Medium and One Pot Synthesis of 1,2,4‐Triazolo(4,3‐a)1,3,5‐triazines

Abstract

A multi‐component condensation of substituted phenylthiourea/urea, aqueous formaldehyde and substituted aromatic/heterocyclic amines lead to 2‐thioxohexahydro‐1,3,5‐triazines (4) in aqueous medium under microwave irradiation in 30–60 sec in quantitative yield with reasonable purity. Further, triazolo[4,3‐a]triazines were also prepared by a one‐pot reaction of ‘in situ’ synthesized triazinyl hydrazine (7) with CS₂ (9).     

Three‐Component,One‐Pot Synthesis of Pyrazolo[3,4‐b]pyridine Derivatives in Aqueous Media

6‐Amino‐4‐aryl‐5‐cyanopyrazolo[3,4‐b]pyridines were synthesized by a three‐component reaction of aromatic aldehydes, malononitrile, and 5‐amino‐3‐methyl‐1‐phenylpyrazole using sodium 1‐dodecanesulfonic (SDS) as catalyst in aqueous media. The reaction has the advantages of good yields, less pollution, ease of separation, and environmental friendliness.     

Cation‐Exchanged Resins: Efficient Heterogeneous Catalysts for Facile Synthesis of 1‐Amidoalkyl‐2‐naphthols from One‐Pot,Three‐Component Condensations of Amides/Ureas,Aldehydes, and 2‐Naphthol

One‐pot, three‐component condensation of 2‐naphthol, amides/ureas, and aldehydes takes place smoothly in the presence of cation‐exchange resins to afford the corresponding 1‐amidoalkyl‐2‐naphthols in good yield. Indion‐130 is found to be the best catalyst for the reaction and is recyclable. The method is simple, solvent free, and involves a short reaction time.     

Microwave‐Assisted Synthesis of 10‐(Phthalimidoalkyl)‐halosubstitutedpyrido [3,2‐b][1,4]‐benzothiazine in Dry Media

N‐Alkylation of 10H‐9‐fluoropyrido[3,2‐b][1,4]‐benzothiazine 5a, 10H‐7‐fluoropyrido[3,2‐b][1,4]‐benzothiazine 5b, and 10H‐7‐chloropyrido[3,2‐b][1,4]‐benzothiazine 5c with different N‐(bromoalkyl)phthalimides using anhydrous K₂CO₃ and tetrabutylammonium bromide (TBAB) under dry conditions with microwave irradiation leads to the formation of 10‐(phthalimidoalkyl)‐halosubstitutedpyrido[3,2‐b][1,4]‐benzothiazine (6a–f) along with some unidentified product. Compound 5a is a new azaphenothiazine derivative and was obtained from hitherto unknown 2‐acetylamino‐3‐fluorophenyl‐3′‐nitro‐2′‐pyridylsulfide 4a via Smiles rearrangement. Compound 4a is required for the synthesis and has been prepared starting from 2‐amino‐3‐fluorobenzenethiol 1a in three steps.     

KHSO4 · H2O/SiO2‐Catalyzed,One‐Pot,Solvent‐Free Synthesis of Pyrazolines,Tetrahydrocarbozoles and Indoles using Microwave Irradiation

A new high‐yielding, operationally simple, solvent‐free, and mild method for preparation of pyrazolines, tetrahydrocarbazoles, and indoles has been developed using KHSO₄ · H₂O impregnated on SiO₂. The reactions have been probed under microwave irradiation (MWI), and ultrasonic and thermal conditions, employing different solid supports. The data revealed that KHSO₄ · H₂O impregnated on SiO₂ under MWI provides the best yields in a shorter time under solvent‐free reaction conditions.     

Clean,One‐Pot Synthesis of 4H‐Pyran Derivatives Catalyzed by Hexadecyltrimethyl Ammonium Bromide in Aqueous Media

Abstract

An efficient and convenient synthetic route to 4H‐pyran derivatives in water in the presence of hexadecyltrimethyl ammonium bromide (HTMAB) as catalyst is described. This method provides several advantages such as environment friendliness, high yields, and a simple workup procedure. In addition, water was chosen as a green solvent.     

Montmorillonite K10 Clay: An Effective Solid Catalyst for One‐Pot Synthesis of Polyhydroquinoline Derivatives

An efficient one‐pot four‐component coupling process for the synthesis of polyhydroquinoline derivatives catalyzed by montmorillonite K10 clay is described. This procedure has such advantages as short reaction time, high yields, and simple workup. The catalyst could be reused several times and keeps its initial activity in the recycle reactions.     

Catalyst-Free Synthesis of α,α-bis(4-Hydroxycoumarin-3-yl)toluene in Aqueous Media Under Microwave Irradiation

An efficient catalyst-free synthesis of α,α-bis(4-hydroxycoumarin-3-yl)toluene was performed by the reaction of 4-hydroxycoumarin with aromatic aldehydes in aqueous media under microwave irradiation. The reaction was completed in short reaction time of 8–10 min with high yields of 76–94, was environmental benign, and had easy workup. Their structures were confirmed by IR spectra, ¹H NMR, ¹³C NMR, and elemental analysis.     

Cation‐Exchange Resins: Efficient Heterogeneous Catalysts for Facile Synthesis of Dibenzoxanthene from β‐Naphthol and Aldehydes

β‐Naphthol reacts with alkyl and aryl aldehydes in the presence of Indion‐130 to give 14‐alkyl/aryl‐14H[a,j]dibenzoxanthenes in good yield.     

One-Pot Tandem Synthesis of β-Trimethylsilyloxy Thioesters from Thioacids,Epoxides, and HMDS Catalyzed by Silica Gel Under Solvent-Free Conditions

A procedure for one-pot preparation of β-trimethylsilyloxy thioesters from epoxides, thioacids, and hexamethyl disilazane (HMDS) in the presence of silica gel under solvent-free condition was developed. The desired silylated products were isolated in good to excellent yields after silica-gel column chromatography.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Simple and Convenient One‐Pot Synthesis of Benzimidazoles and Benzoxazoles using N,N‐Dimethylchlorosulfitemethaniminium Chloride as Condensing Agent

N,N‐Dimethylchlorosulfitemethaniminium chloride (SOCl₂‐DMF) has been found to be an efficient reagent for the one‐pot synthesis of benzimidazoles and benzoxazoles in excellent yield by condensation of carboxylic acids with o‐phenylenediamine/2‐amino‐phenol.     

Bifunctionalized Allenes,VII: Two Methods for One‐Pot Synthesis of Sulfonyl‐Functionalized Allenecarboxylates and Phosphorylated Allenes

Two new approaches to the synthesis of sulfonyl‐functionalized allenecarboxylates and phosphorylated allenes are described. 2‐Sulfonyl‐alka‐2,3‐dienoates were readily prepared in an one‐pot reaction by [2,3]‐sigmatropic rearrangement of sulfinato‐substituted 2‐alkynoates, in situ generated from ethyl propynoate and subsequent treatment with lithium diisopropyl (LDA), ketone, trimethylchlorosilane (TMSCl), and the corresponding sulfinyl chlorides. Preparation of 1‐sulfonyl‐alka‐1,2‐dienephosphonates and ‐1,2‐dienyl phosphine oxides consists of the reaction of the lithio compounds, in situ generated from phosphorylated allenes and LDA, with the corresponding sulfonyl chlorides.